Wave attenuating large ocean platform

ABSTRACT

A large deck area floating platform with wave attenuating outriggers provides equivalent payload and deck operating area to a fixed, piled, and jacketed platform alternative for coastwise and offshore applications. The floating platform integrates large deck areas for industrial applications with a main ship-shaped hull and a submersible system of outriggers and column risers to form a stable, transportable, and structurally sound industrial facility that may be tuned hydro-dynamically to attenuate wave forces on the moored structure. The platform provides from 2 to 10 acres of weather deck and associated superstructure space, a ship-like hull, and direct subsea access via enclosed areas between the main hull and outriggers. Through the medium of differential ballasting, the displacement and freeboard of the facility may be adjusted to maintain hydro-dynamic tuning for changing wave conditions or to provide additional freeboard for storm survival.

This invention was made with Government support under Contract No. FA9200-06-C-0022 awarded by the Department of the Air Force. The Government has certain rights in this invention.

FIELDS OF THE INVENTION

The invention relates to offshore floating platforms for energy, military, oil & gas, heliport, and chemical processing applications.

BACKGROUND OF THE INVENTION

Fixed jacketed structures have long been used in the offshore industry to support hydrocarbon production and processing facilities. With the expansion of the oil industry from coastwise exploration and production to the outer continental shelf, these fixed structures have been built to ever increasing depths at ever increasing costs.

Despite their ubiquitous presence, the jacketed structure has major drawbacks for certain applications; chief among which is that it cannot be relocated. In addition, the jacketed structure does not have the payload capacity for storage and processing of large volumes of liquids. Jacketed platforms also do not have the compartmentalization and subdivision necessary to provide redundancy in the event of catastrophic events such as subsea blasts and overhead explosions.

The challenge to designing and building equivalent floating structures are the wave forces acting on the structure, the internal forces and moments created by those wave forces on the structure, the requirements for a mooring system and the inherent need for sufficient compartmentalization to provide survivability in case of flooding.

Wave forces are typically related to the pressure field of ocean waves under the free surface of the ocean as seen by the floating body's hull (Froude-Krylov), the interaction of impinging waves on the floating structure's outer perimeter surface (wave reflection and refraction), and the potential creation of standing waves within area enclosed by walled structure (standing waves). Motion of the floating body itself will generate wave systems (wave diffraction), and in a most general sense there is a complex interaction of irregular ocean waves and a floating structure generally referred to as Ship Motions or Ship Dynamics.

For many years, the offshore oil industry has relied upon semi-submersible structures to mitigate these interactive effects. However structures designed along these lines are of necessity limited in terms of payload capacity because the combined area of the vertical columns provides a very low ratio of added weight to hull submergence (so called “tons per inch immersion” or “TPI”) and vulnerability to damage in the submersible hulls make residual stability due to flooding highly problematic (so called “damaged stability”). For a semi-submersible structure, the very features that make the unit more transparent to ocean waves contribute to its vulnerability to damage, and low variable payload capacity in a practical operational setting. These units are typically used for exploration rather than as floating industrial facilities because variable weights can be kept to a minimum.

Needs exist for improved offshore structures that are relocatable, are less vulnerable to damage, and have a high variable payload capacity that allows for utilization as industrial facilities in practical operational settings. Needs exist for improved offshore industrial facilities with the compartmentalization and subdivision necessary for redundancy and with the payload capacity for storage and processing of large volumes of liquids.

SUMMARY

A transportable coastwise or offshore industrial facility requires large deck areas coupled with large variable storage requirements. Examples of this type of facility include facilities for LPG processing and storage, for use as heliports or wind farms, for ocean energy (such as an Ocean Thermal Energy Conversion (OTEC) plant, offshore wind turbines, or wave energy harvesting power plants), for use as offshore military test and evaluation platforms, or for chemical and hydrocarbon distribution through subsea pipelines and risers. These facilities may be assembled in protected waters using established construction practices for structural steel or light weight concrete pre-stressed and post-tensioned hybrid structures, then towed out and moored at a permitted coastwise or offshore site.

Unlike fixed structures employing pilings and jacketed frames for support, the floating industrial facility may be relocated as required. The facility is of interest to a number of industries, as it has a wide variety of commercial offshore and coastal applications as mentioned, including in LPG processing and storage, as a heliport or wind farm, for ocean energy, as an offshore military test and evaluation platform, and in chemical and hydrocarbon distribution processing.

A large deck area floating platform with wave attenuating outriggers provides equivalent payload and deck operating area to a fixed, piled, and jacketed platform alternative for coastwise and offshore applications. The floating platform integrates large deck areas for industrial applications with a main ship-shaped hull and a submersible system of outriggers and column risers to form a stable, transportable, and structurally sound industrial facility that may be “tuned” hydro-dynamically to attenuate wave forces on the moored structure.

In its most general configuration the Wave Attenuating Large Ocean Platform (WALOP) provides from 2 to 10 acres of weather deck and associated superstructure space, a ship-like hull, and direct subsea access via enclosed areas between the main hull and outriggers. Through the medium of differential ballasting, the displacement and freeboard of the facility may be adjusted to maintain hydro-dynamic tuning for changing wave conditions or to provide additional freeboard for storm survival.

Throughout this application, the word “cylinder” is used to encompass geometric prisms as well as cylinders, such that the shapes referred to as cylinders may have circular, ellipsoidal, or n-sided polygonal cross sections. These and further and other objects and features of the invention are apparent in the disclosure, which includes the above and ongoing written specification, with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more particularly described in conjunction with the following drawings wherein:

FIG. 1 is an isometric view of the Wave Attenuating Large Ocean Platform or WALOP moored in a notional operational setting.

FIG. 1 a shows an operational variant of FIG. 1

FIG. 2 discloses the general arrangement of WALOP structure below the platform level which itself has been removed from view for clarity.

FIGS. 3 a-3 c are cross sectional views taken from FIG. 2.

FIG. 4 is an overhead diagram showing a variant of FIGS. 2 & 3 wherein only one ship-like hull is utilized.

FIGS. 5 a-5 c are cross sectional views taken from FIG. 4 and illustrate different prismatic cross sectional geometries arranged to accommodate different industrial purposes and methods of assembly as well as providing different depths of freeboard or submergence to meet hydrodynamic response criteria.

FIG. 6 a is an isometric view diagram of a WALOP with a single hull and cylindrical outriggers and columns having circular cross sections.

FIG. 6 b is a front view of the WALOP of FIG. 6 a, FIG. 6 c is a cross section of the WALOP of FIG. 6 a along line A-A, and FIG. 6 d is a side view of the WALOP of FIG. 6 a.

EXPLANATION OF REFERENCE NUMERALS

-   Wave Attenuating Large Ocean Platform (WALOP); Find Number 1,     overall assemblage and outfit of a large deck area (nominally 2 to     10 acres) floating industrial facility. -   Main Hull: Find Number 2; made up of a Principal Main Hull and     (optionally) two orthogonal Hull Sections, provides essential water     plane area to accommodate variable industrial loading at near     constant draft. The Main Hull also provides liquid storage including     Ballast Tanks -   Principal Main Hull: Find Number 2 a; the principal longitudinal     ship-like floating structure. -   Hull Sections: Find Number 2 b; made up of two hulls each attached     orthogonally to the Principal Main Hull at or near its midship. -   Elbow Assemblages: Find Number 3; assembly of one or more Horizontal     Prismatic Cylindrical Outriggers with one Vertical Prismatic     Cylindrical Column. Nominally there are four Elbow Assemblages on a     WALOP. -   Horizontal Prismatic Cylindrical Outrigger: Find Number 4; a     submersible or semi-submersible cylinder lying respectively beneath     or penetrating the free surface water plane and attached at one end     to the Main Hull and at the other to a Vertical Prismatic     Cylindrical Column. They may be of any prismatic shape and have, for     example, circular, rectangular, or ellipsoidal cross sections. These     cylinders provide draft or freeboard as required to attenuate wave     energy and add hydrodynamic mass and damping to the WALOP system.     These cylinders also contain the Ballast Tanks and may carry liquid     payload. -   Vertical Prismatic Cylindrical Column: Find Number 5; structurally     they provide the connection between the Horizontal Outriggers and     the platform deck structure. They also provide water plane area and     inertia to aid in tuning the WALOP for hydrostatic and hydrodynamic     response to the ocean wave environment. -   Platform Deck: Find Number 6; structurally connects the Main Hull     with the Vertical Columns and spans the open area between the Elbow     Assemblages and the Main Hull. This is the structural member     integrating the Horizontal Outriggers to the Main Hull. The Platform     Deck may be supported by a system of truss work, and/or be the lower     level of a Superstructure. -   Weather Deck: Find Number 6 a; uppermost exposed deck of the     Superstructure -   Superstructure: Find Number 6 b; structure including intermediate     decks and spaces between the Platform Deck and the Weather Deck. If     there is no such structure then the Platform Deck is the Weather     Deck and no Superstructure exists. -   Mooring Stations: Find Number 7; normally there will be four mooring     stations on a WALOP with one station at each of the four cardinal     points on the Main Hull. Each station may consist of a number of     mooring winches, pullers, chain and associated handling equipment on     each leg of the mooring system. Alternatively the entire WALOP may     be moored on a single point mooring and permitted to weathervane in     the sea conditions. -   Ballast Tanks: Find Number 8; accommodate variable ballast system.     Tanks will ordinarily be within the Main Hull and the Horizontal     Outriggers. -   Permeable Cell Facings: Find Number 9; cavities for air pockets     designed to dissipate wave energy in the run-up of reflecting waves     on vertical sides of the Main Hull and wall sided Horizontal     Outriggers. -   Transverse and Longitudinal Bulkheads: Find Number 21; these     vertical internal hull plane structures provide watertight     subdivision (generally) and additional structural continuity to     outer shell structural integrity to resist global and local     hydrostatic and dynamic ocean forces. -   Deck: Find Number 22; in naval architectural meaning these     horizontal plane structures provide further internal subdivision for     survivability of the hull if flooded as well as boundaries for     tankage and spaces for machinery, cargo, or other industrial     applications. -   Attachment Bossing: Find Number 23; the attachment bossing is a     structural protrusion to hull structure which serves as a fairing     for joining other structure. The connection develops bi-directional     strength and the cavity formed between the connected structures is     sealed to prevent flooding. -   Strut: Find Number 61; a vertical member of the support truss for     the Platform Deck. -   Bracing: Find Number 62; a diagonal member of the support truss for     the Platform Deck. -   Lower Chord: Find Number 63; lower horizontal truss member of the     Platform Deck support structure. -   Box Girder: Find Number 64; rectangular closed cell structure which     forms the top chord in the Platform Deck support structure. -   Water Line: Find Number 101; indicates the water level, which will     vary depending on characteristics of the WALOP. -   Low Water Line: Find Number 103; Indicates the lowest level the     water line can reach.

DETAILED DESCRIPTION

A floating platform has sufficient geometry to support a vast deck area (for example 450′×450′) for industrial operations along with a hull structure (for tankage, machinery and accommodation as desired) and an integrated system of vertical columns with attachment outriggers between the main hull and vertical columns configured to provide margins of stability in roll and pitch an order of magnitude beyond that minimally required. Wave forces on the floating structure are mitigated by the system of perimeter surface piercing (or submerged) outriggers that are “tuned” hydrodynamically to reduce the coefficient of wave transmission by targeting their depth of submersion to a given wave climate and prevailing sea condition.

Depending upon the amplitude, steepness, and frequency of the impinging wave, the depth of water, and the cross sectional dimensions, freeboard and surface of the cylinder, the transmission coefficient (ratio of the wave height of the impinging wave to the transmitted wave) may be reduced by 50%. In wave energy terms this 50% reduction in height converts to a 75% reduction in transmitted wave energy. The remaining wave energy converts to reflected wave energy and energy absorption in the surface cavities of the cylinder.

Side walls of the outrigger and hull structure subject to generating standing waves are covered with wave absorbing cell cavities in a manner similar to current practice for lining vertical breakwaters for harbor jetties. The entire platform may be moored in a cardinal array at a chosen orientation to prevailing wind and sea, thereby making it possible to greatly reduce the 6 degrees of freedom motions exhibited by all floating structures (surge, sway, heave, roll, pitch and yaw) as well as to mitigate the forces of steady drift due to wave reflection. Alternatively, mooring may be accomplished using a single point mooring, with or without its own riser application. Single point mooring with a riser application incorporates a subsea riser through a single point mooring buoy so that the platform would be able to weathervane and still load and discharge liquid cargo, much like a single point mooring system used for tankers.

The main hull may be a specially designed vessel purpose built or converted for the industrial application desired. It may be characterized as being “ship like” in principal dimensions (i.e. with a relatively large length to beam ratio of around 5 to 15, and a sufficient depth to draft ratio to provide for variable payloads and depth of submergence-around 1.5 to 3 for the main hull depending on the amount of variable payload desired). Materials of construction include but are not limited to structural steel or lightweight marine grade concrete structures as well as a hybrid combination of the two. Other materials and combinations like fiberglass reinforced polyester (so called FRP) are possible especially for smaller applications.

The internal hull structure may be configured with storage and/or ballast tanks, internal accommodation spaces, machinery, and electrical and mechanical equipment typical of an industrial facility. The main hull provides the bulk of the water plane area required to have a high ratio of variable weight to change in draft (a high numerical value of tons per inch immersion) as well as the longitudinal stiffness for hull pitching motions (so called “longitudinal metacenter” or KMl). The main hull depth provides the design freeboard at the operating draft, and it is subdivided as required for reserve buoyancy due to flooding. The main deck may be configured with piping runs, anchor handling equipment, or other industrial configurations (or none at all) as required for the industrial application. Typically the main deck is below the operations deck and optional superstructure as described below.

Whether purpose built or converted, the main hull is configured with large scale integral structural bossing which is used to attach the outriggers to the main hull. The outriggers may have the shape of any prismatic cylinder and may have circular, ellipsoidal, rectangular, or trapezoidal cross-sections, or any other shape required for wave “tuning” and ballast/storage capacity requirements for industrial operations. They and are generally attached forward, amidships and aft along the main hull, port and starboard, and orthogonal to the hull's longitudinal axis of symmetry.

The shape of the outriggers affects the wave hydrodynamic pressure and velocity field and the transmission of wave energy past the barrier. Freeboard in the case of a surface piercing outrigger affects wave overtopping and the reflected wave energy. In addition, some geometries such as circular cross sections have higher load bearing capability per unit weight than flat panels of structure. In the tradeoff of cargo carrying capacity, overall platform stability and survivability as well as wave attenuation there are efficiencies to be gained or lost depending upon overall design needs. There is no one perfect design solution.

At the lateral outboard termination of these outriggers surface piercing vertical columns are attached in a manner well established in the marine industry for semi-submersible construction. Tying these columns together longitudinally are a similar set of surface piercing (or submerged) outriggers so the surface piercing columns are attached at a fixed distance from the main hull laterally, and among themselves longitudinally by the system of outriggers.

In the jargon of this invention, the orthogonal outriggers that incorporate a vertical surface piercing column are called an “Elbow”. The attachment of these elbows to the main hull requires neither a dry-dock nor a specialty graving dock. Rather, the technology exists to make this attachment in-situ in quiescent waters using established techniques like those that follow. For post tensioning lightweight marine concrete structures, the technique is to use a series of massive tendons fed through a system of internal ductwork embedded within the concrete structure. In the case of steel construction, temporary cofferdams may be used by the builder to provide a dry environment for full penetration welding and classification society inspection of the attachment welds. On a smaller scale, mechanical fastenings may be employed as well. These mechanical fastenings may include large diameter machined bolts with nuts set in place to a predetermined elongation via use of hydraulic torque generating equipment. In joining the structures a system of alignment pins and guides are typically employed to make up the precise fit of faying surfaces as hydraulic jacks or pullers are used to move the structures together. This system of alignment pins and guides typically consists of large diameter machined guide pins attached to one structure at critical alignment locations (male connection) and a corresponding set of receiving guides (female connection) on the structure to be connected.

The surface piercing vertical columns may themselves be any convenient shape and not necessarily prismatic in geometry. However, the platform relies upon each column's water plane area to contribute to the floating structure's overall transverse hydrostatic and hydrodynamic stability (so called “transverse metacenter”, KMt) as well as to augment the overall floating platform's high value of TPI.

It is well known that the second moment of area of these surface penetrations about the main hull's generating longitudinal axis adds to the main hull's own transverse moment of inertia to form a combined value for the floating structure taken as a whole. Likewise the longitudinal moments of these columns' areas adds to the overall floating platform's longitudinal stability (KMl).

It is apparent then that judicious location and adjustment of the columns' cross sectional area allows the floating platform to be simultaneously optimized for longitudinal and transverse stability when the overall platform's mass center of gravity is factored into play. Accordingly, the dynamic response of the structure to the design ocean wave environment at the operations site may be adjusted in the design stage to provide the optimal transverse and longitudinal metacentric heights (GMt and GMl respectively). The metacentric height not only plays an important role in determining the floating platforms natural response frequency to external excitation forces (waves), but is also a very important measure of the unit's ability to survive damage that causes flooding.

For a lightly damped single degree of freedom model of the floating body, it can be shown that the platform's natural frequency of dynamic response to the ocean wave environment is directly related to the square root of the floating body's transverse (GMt) and longitudinal (GMl) metacenter, which along with the body's displacement constitutes the restoring coefficient to the steady state equation of motion of the body in either roll or pitch. Further, GMt and GMl can be approximated by the second moment of area inertia of the surface piercing geometry of the body in roll (It) and pitch (Il) about the respective rotational axes. These quantities may then be equated (It=Il) and used in the design of the platform to shift the platform response to a resonant frequency outside of the prevailing sea conditions.

Also coming into play in this calculation is the polar moment of inertia of the body itself, which can be taken as a function of the mass of the body and its radius of gyration. If the system is considered to be a lightly damped single degree of freedom (SDOF) model, as roll or pitch motion is generally taken for illustration purposes, it can be shown that by judicious selection of a ratio of length to beam for the main hull and area geometries and centroidal distances of surface piercing horizontal outriggers and vertical columns that the resonant frequency of the unit may be moved to an excitation frequency lying outside the domain of frequencies in the design sea way.

In addition to the main hull, outriggers and vertical columns (elbows), in its most general form the overall floating platform is tied together at the platform level by means of large box girders which connect the upper ends of the vertical columns to the main hull. These box girders, each with a bottom chord structure of large diameter pipe and other truss components (such as tubular vertical and diagonal braces), form the top flange of the entire floating structure to transmit and absorb so called “hull girder” and secondary shear and moment forces caused by hydrostatic and dynamic loads. Trusses connect orthogonally at “K” type joints to provide bi-directional loadbearing capacity.

The box girders and associated decking run from the extreme port to extreme starboard side of the floating platform as well as longitudinally forward and aft, thus providing structural continuity to both lateral and transverse floating platform shear and bending. Within the structural geometry of the invention, both the outriggers and platform box girders are tied together to form a “space frame”-like array of load carrying members that provide the floating platform's overall structural integrity.

Platform decking runs between the main box girders, and it is this decking that supports penetrations from subsurface risers and other vertical access to the seafloor (if desired). Atop this foundation decking may be constructed a superstructure of decking incorporating industrial, power, hydrocarbon or chemical processing facilities, or alternatively test and evaluation targets, ocean or wind energy recovery devices, or aviation operating platforms and hangars (to name but a few).

Taken in total, a floating platform and industrial facility is provided that incorporates large platform areas for industrial equipment, abundant storage and tankage (as desired) for chemical and industrial processes, and a main hull (or orthogonal hulls if desired) for mechanical, electrical, accommodation or other spaces desired to be located out of the weather. This platform may be moored using conventional mooring systems at predetermined coastwise or offshore sites, or positioned using a single point mooring as an alternative. In addition, it is possible for the designer to “tune” the floating platform's hydrodynamic characteristics to minimize ship dynamics and attenuate impinging waves in the selected design ocean environment.

For survivability considerations, in 100 year or other storm scenarios, the freeboard may be increased by discharging ballast contained in tanks or pumping processing material to shore or a safe haven during storm preparation activities. Prior to storm arrival any risers can be lowered to the sea floor for safety and the mooring lines adjusted to assist in riding out the event.

Benefits and unique features of the platforms described include:

-   1. A Wave Attenuating Large Ocean Platform (WALOP) 1 of unique form     that may be hydrodynamically tuned to the local wave environment to     attenuate the forces and moments imposed by the seaway on the     overall structure. The tuning is accomplished by design and     operational variation in displacement and mooring tension such that:     -   Metacentric height of the WALOP 1 in roll (GMt) and pitch (GMl)         may be adjusted by design such that its natural period of         oscillating motion falls outside the range of predominant wave         periods in the proposed coastwise or offshore operational         setting.     -   The Vertical Prismatic Cylindrical Columns 5 provide additional         water plane inertia to the Main Hull 2 for oscillatory         rotational motion (KMt and KMl) of the WALOP 1 taken as a whole.     -   Horizontal Prismatic Cylindrical Outriggers 4 provide         submersible added mass and damping geometry to modulate         oscillatory motion. Freeboard or depth of the Elbow Assemblage 3         may be adjusted operationally to dissipate wave forces before         they reach the Main Hull 2.     -   Elbow Assemblage 3 may be designed and adjusted for submergence         or freeboard to break steep wave crests impinging on the         structure before this wave energy impacts upon the Main Hull 2.     -   Wave reflection may be dissipated by use of Permeable Cell         Facings 9 mounted on the vertical sides of the Elbow 3 and Main         Hull 2.     -   Dynamic response of the structure in surge, yaw and sway may be         modulated operationally by variation in mooring line scope and         corresponding stiffness at the various Mooring Stations 7. In         this manner the mooring array can be varied at each cardinal         direction to tune the entire mooring system of WALOP.     -   Sheltered areas to leeward of the approaching wave system for         support or supply vessels to lie along side and load or         discharge cargo to overhead cranes (if desired).     -   Sheltered pools of water within the perimeter of the Elbow 3 and         Main Hull 2 are available through which risers and other sub-sea         fluid (liquid or gas) piping or electrical transmission lines         may access a sea floor distribution system. -   2. A unique structural design concept connecting the multilevel deck     structure to the buoyant hull and outrigger structure via Vertical     Prismatic Cylindrical Columns 5 such that:     -   The multilevel deck Superstructure 6 b forms the upper flanges         and box girder of the structural geometry to carry global         bending, shear and torsional loads.     -   The arrangement of Horizontal Outriggers 4 forms the lower         flange of structural geometry to carry global bending, shear,         and torsional loads.     -   Main Hull 2 structure(s) supports the Platform Deck 6 and         terminates the loads carried by the horizontal prismatic         cylinders 4 at structural bossing.     -   Main Hull 2 carries torsional moments produced by the Elbow         Assemblages 3 of Horizontal Outriggers 4 and Vertical Columns 5.     -   The Horizontal Outrigger 4 may be supported at mid span by use         of diagonal lower chord truss bracing tied into the Vertical         Columns 5 at the multilevel deck Superstructure 6. -   3. A Platform Deck 6 a of large area (nominally 2 to 10 acres)     suitable for:     -   Layout of Superstructure 6 b and industrial equipment for         chemical, gas or hydrocarbon processing facilities with sub-sea         fluid transmission lines, or optionally, power generation (wind,         wave, natural gas, geothermal, or hydrocarbon) facilities with         subsea power transmission lines, or optionally, clear deck area         for military or commercial test or flight operations.     -   Elevator or stair tower access below the Weather Deck 6 a to         interior Superstructure spaces 6 b. Direct vertical sub-sea         access below the Superstructure 6 b to the sea floor in the         sheltered pools of water contained within the Elbow Structures 3         and the Main Hull 2 perimeter.     -   Crane pedestals located atop the Vertical Columns 5 for         over-the-water cargo handling operations. -   4. An integrated single or orthogonal pair of Main Hulls 2 which     serve the following purposes:     -   Structural support for Platform Deck 6 and the principal         attachment point for the Horizontal Outriggers 4.     -   Tankage and piping for liquid or gas storage when using a tanker         like main hull structure.     -   Bow and stern platforms for Mooring Stations 7.     -   Accommodation, recreation and office facilities either in the         deckhouse of a converted vessel or below deck in a purpose built         ship-like structure. -   5. An single or orthogonal pair of Main Hulls 2 integrated with the     Elbow Structures 3 serve the following hydrostatic purposes:     -   Within the Main Hull 2 large storage volumes permit variable         liquid or solid payloads at constant draft and trim conditions,         and in addition, Horizontal Prismatic Cylindrical Outriggers 4         provide additional means to store Ballast Tanks 8 to accommodate         differential ballasting to maintain either constant displacement         at variations of hull and deck loading or to vary freeboard and         depth for local sea conditions.     -   Variable displacement capabilities with a large water-plane         capacity for added cargo payloads weights with small changes in         draft (TPI) and hydrodynamic tuning for sea conditions.     -   Ability to change the freeboard and draft in preparation for         storm conditions by discharge from the Ballast Tanks 8     -   Redundant Internal Bulkheads 21 and Decks 22 enhance         survivability of the structure in case of flooding due to hull         damage.

In the several figures, like reference numerals refer to like parts having like functions. FIG. 1 shows a Wave Attenuating Large Ocean Platform 1, which is fundamentally a buoyant structure including an orthogonal Main Hull 2 together with four symmetrically placed Elbow Assemblages 3, each of which includes two orthogonal intersecting Horizontal Prismatic Cylindrical Outriggers 4 and a Vertical Prismatic Cylindrical Column 5. Atop this floating structure is a Platform Deck 6 (approximately the square of the Main Hull 2 length) which is structurally integrated into the Main Hull 2 and the four Elbow Assemblages 3. Integral to the Main Hull 2 are Mooring Stations 7 located at each end of each hull, which taken together form cardinal points for a four station mooring system.

FIG. 1 a shows a variant of this arrangement that provides four independent deck structures for operational redundancy. Not shown in FIG. 1 or 1 a but included in FIGS. 3 a, 3 b, and 3 c, are Ballast Tanks 8 located internally within the Main Hull 2 and the Horizontal Outriggers 4. Also shown are optional Permeable Cell Facings 9 that can be placed on the vertical sides of the Hull 2 and Outriggers 4.

The particular configuration shown in FIG. 1 is repeated in plan view in FIG. 2 (with the Platform Deck 6 removed for clarity). This configuration was originally designed for construction in light weight pre-stressed and post tensioned concrete; however it could as easily be designed and constructed in steel or, for smaller scale structures, fiberglass.

The orthogonal Hull 2 consists of a Principal Main Hull 2 a which is constructed ashore or in an ordinary graving dock to the overall length of the platform. The Principal Main Hull 2 a includes Internal Transverse and Longitudinal Bulkheads 21 and Decks 22 (FIGS. 3 b, 3 c) as necessary to provide subdivision, cargo tankage, industrial accommodations, and hull girder strength to the ship-like structure. The Principal Main Hull 2 a also includes an array of Attachment Bossings 23 located amidships and near the bow and stern, which are used to provide structurally viable attachment brackets for the orthogonal structure.

In this particular concrete configuration the orthogonal structure is made up of shorter Hull Sections 2 b which are joined in the water using differential ballasting to engage alignment pins and mechanical fastening to locally join the structure. Continuity of hull strength for hull girder bending and torsion are accomplished using post-tensioning tendons to compress the connection joint. For steel construction, a similar alignment process is followed, however the structure is welded together, using a series of surface piercing construction cofferdams to provide a dry environment to complete the welding to classification society standards. For either construction method, once jointed at amidships the orthogonal Hull 2 displays the structural characteristics of an integrated orthogonal intersection with bi-directional structural continuity in global bending, shear and torsional loads.

Similarly to the construction and joining of the Hull 2 components the Horizontal Outriggers 4 are built ashore or in a graving dock and then attached to the Vertical Column 5 to form an Elbow Assemblage 3. This latter assembly is connected to the Attachment Bossing 23 near the ends of the Hulls 2 a and 2 b. The process of alignment pins and mechanical fastening is of similar scale to that of the orthogonal intersection of the Principal Main Hull 2 a and Hull Sections 2 b. The process of joining the Elbow 3 a to the Hull 2 is repeated three times (3 b, 3 c, 3 d) so as to form the FIG. 2 view.

Following the integration of floating structure by this or several other alternative means, the Platform Deck 6 is built over the substructure configuration of Hull 2 and Elbows 3 a, 3 b, 3 c, and 3 d. The Platform Deck 6 may be one Weather Deck 6 a or a number of deck levels forming a Superstructure 6 b, and there are a variety of methods through which its structure may be tied in with the upper level of the Hull 2 and Elbows 3.

Note from FIG. 2 that the configuration of the structure naturally results in sheltered pools of water. Although the quiescent nature of these pools makes them ideal for risers or pipelines emerging from the water, steps must be taken to allow the Platform Deck 6 to somehow span them. For example, the Platform Deck 6 can be structurally connected into the Hull 2 using a series of structural Struts 61 and structural Bracings 62 as seen in FIGS. 3 a-3 c to provide sufficient clearance over the water to meet the operational freeboard requirement. The Platform Deck 6 span over the pools of water may also be supported using a truss system with a Lower Chord 63 of structural steel tubes and a system of structural steel Box Girders 64 at the deck level as seen in FIG. 3 c.

Once the Platform Deck 6 has been structurally integrated with the Vertical Columns 5 and Main Hull 2, the WALOP primary configuration is complete and it is then possible to finalize the outfit with a Superstructure 6 b, additional Mooring Stations 7 or Ballast Tanks 8, or any other appurtenances required to configure the WALOP for its intended use, such as cargo tankage, industrial spaces, cranes, risers, or processing equipment. Upon completion, the WALOP may be towed to its operations site, moored with a site specific system and ballasted to its operational draft.

This WALOP concept lends itself to a variety of naval architectural geometries that can be selected based upon prevailing sea conditions and the operational mission. FIG. 4 shows a variation of the orthogonal hull geometry in which only the Principal Hull 2 a is utilized. In this configuration, two additional Outriggers 4 e and 4 f and associated Columns 5 e and 5 f have been tied into the assembly of Elbows 3 a through 3 d to substitute for the shorter Hull Sections 2 b identified in the previous configuration above. There are now six Columns 5 and ten Outriggers 4 as shown in FIG. 4. These are then tied to one another and to the Main Hull 2 by means of the Platform Deck 6 in a manner similar to the description above.

FIGS. 5 a-5 c are cross sectional views taken from FIG. 4 along the lines indicated in FIG. 4, and illustrate different prismatic cross sectional geometries arranged to accommodate different industrial purposes and methods of assembly as well as providing different depths of freeboard or submergence to meet hydrodynamic response criteria.

FIG. 6 a shows a WALOP 1 with a single hull 2 and outriggers 4 and columns 5 having circular cross sections. FIG. 6 b is a front view, showing the water line 101, which may vary depending on local conditions and the configuration of the WALOP, and low water line 103. FIG. 6 c is a cross section along line A-A and FIG. 6 d is a side view.

In one embodiment, in FIG. 6 b the horizontal distance from the left side of the first vertical column 5 to the right side of the last vertical column 5 is 450′, and the horizontal distance between each end vertical column 5 and the tip of the mooring station 7 is 50′, for a total length from mooring point tip to mooring point tip of 550′. The height of each vertical column 5 is 75′, the diameter of each vertical column 5 is 40′, and the diameter of the horizontal outrigger 4 and distance between the water line 101 and low water line 103 is 30′. The distance between centers of the vertical columns 5 is 205′ and the horizontal distance from the end vertical column 5 to its corresponding mooring point tip is 70′. The hull 2 is 65′ high and the flat portion is 15′ high with the angled portion 60′ high.

In FIG. 6 c, the distance between centers of the horizontal outriggers 4 is 210′ and the horizontal distance between the center of the end horizontal outriggers 4 and corresponding mooring point tips is 65′. In FIG. 6 d, the vertical columns 5 are 40′ in diameter and 75′ in height, the horizontal outriggers 4 are 30′ in diameter, there are 450′ between the left end of the left vertical column 5 and the right end of the right vertical column 5, and the horizontal distance between the center of each vertical column 5 and the center of the hull 2 is 205′.

It is clear that other geometry may be employed by the naval architect to implement a particular industrial mission with the WALOP invention. The orthogonal Elbows 3 might be curved into a quarter or semi-circular form. In this geometry the Platform 6 would be reduced somewhat in area but structurally and operationally integrated into the Principal Main Hull 2 a.

The invention is not limited to the particular embodiments illustrated in the drawings and described above in detail. Those skilled in the art will recognize that other arrangements could be devised, for example, various different hull and deck geometries and sizes and necessary accompanying support structures and various different outrigger/column geometries. While the invention has been described with reference to specific embodiments, modifications and variations of the invention may be constructed without departing from the scope of the invention. 

1. A buoyant structure, comprising a hull, one or more decks supported by the hull, surface piercing vertical columns, and submersible horizontal outriggers attaching the surface piercing vertical columns to the hull.
 2. The buoyant structure of claim 1, wherein the hull comprises a principal main hull and hull sections, wherein the principal main hull is a longitudinal ship-like floating structure and the hull sections are attached orthogonally to the principal main hull near its midship.
 3. The buoyant structure of claim 1, further comprising one or more mooring stations at one or more ends of the hull.
 4. The buoyant structure of claim 1, further comprising wave absorbing permeable cell facings on sides of the hull or submersible horizontal outriggers.
 5. The buoyant structure of claim 1, further comprising ballast tanks in the hull and submersible horizontal outriggers, wherein differential ballasting can be used to adjust the displacement and freeboard of the buoyant structure to maintain hydro-dynamic tuning for changing wave conditions or to provide additional freeboard for storm survival, or to maintain constant displacement at variations of hull and deck loading.
 6. The buoyant structure of claim 1, wherein the one or more decks comprise four independent deck structures.
 7. The buoyant structure of claim 1, wherein a sheltered pool of water is formed in an area enclosed between the hull and submersible horizontal outriggers and surface piercing vertical columns, allowing direct subsea access.
 8. The buoyant structure of claim 1, wherein the submersible horizontal outriggers are submerged to a depth that tunes them hydrodynamically to reduce their coefficient of wave transmission in a given wave climate and prevailing sea condition.
 9. The buoyant structure of claim 1, further comprising crane pedestals located atop the surface piercing vertical columns for over-the-water cargo handling operations.
 10. The buoyant structure of claim 1, wherein the hull comprises a structure that is ship-like in principal dimensions, having a relatively large length to beam ratio and a sufficient depth to draft ratio to provide for variable payloads and depth of submergence.
 11. The buoyant structure of claim 1, wherein the hull comprises integral structural bossing used to attach the submersible horizontal outriggers to the hull.
 12. The buoyant structure of claim 1, wherein the location and cross sectional area of the surface piercing vertical columns provide the optimal transverse and longitudinal metacentric heights to optimize the longitudinal and transverse stability of the buoyant structure, accounting for the overall mass center of gravity of the buoyant structure, such that the natural period of the buoyant structure's oscillating motion falls outside the range of predominant wave periods in a selected operational setting.
 13. The buoyant structure of claim 1, further comprising box girders connecting upper ends of the surface piercing vertical columns to the main hull, forming a top flange of the buoyant structure to transmit and absorb hull girder and secondary shear and moment forces caused by hydrostatic and dynamic loads, where the submersible horizontal outriggers form a corresponding lower flange.
 14. The buoyant structure of claim 13, wherein the box girders each form the upper chord of a truss system with a large diameter pipe or rectangular steel box girder forming the lower chord of the truss. comprise a bottom chord structure of large diameter pipe and other truss components.
 15. The buoyant structure of claim 13, wherein the box girders and associated decking run from the extreme port to extreme starboard side of the buoyant structure as well as longitudinally forward and aft, thus providing structural continuity to both lateral and transverse floating platform shear and bending.
 16. The buoyant structure of claim 13, wherein the submersible horizontal outriggers and box girders are tied together to form an array of load carrying members.
 17. The buoyant structure of claim 13, wherein the one or more decks comprise platform decking running between the box girders.
 18. The buoyant structure of claim 17, wherein the one or more decks further comprises a superstucture of decking atop the platform decking, which incorporates industrial, power, hydrocarbon or chemical processing facilities, test and evaluation targets, ocean or wind energy recovery devices, or aviation operating platforms and hangars.
 19. The buoyant structure of claim 1, wherein six of the submersible horizontal outriggers are attached forward, amidships and aft along the hull on port and starboard sides, orthogonal to the hull's longitudinal axis of symmetry, wherein the surface piercing vertical columns are attached at lateral outboard terminations of the submersible horizontal outriggers, and wherein four of the submersible horizontal outriggers tie the columns together longitudinally, so that the surface piercing vertical columns are attached at a fixed distance from the hull laterally and among themselves longitudinally by the submersible horizontal outriggers.
 20. The buoyant structure of claim 1, wherein four of the submersible horizontal outriggers are attached forward and aft along the principal main hull on port and starboard sides, orthogonal to the hull's longitudinal axis of symmetry, wherein the surface piercing vertical columns are attached at lateral outboard terminations of the submersible horizontal outriggers, and wherein four of the submersible horizontal outriggers tie the columns longitudinally to the hull sections, so that the surface piercing vertical columns are attached at a fixed distance from the hull laterally and from the hull sections longitudinally by the submersible horizontal outriggers.
 21. The buoyant structure of claim 1, wherein the submersible horizontal outriggers and surface piercing vertical columns are formed into elbow assemblages, each elbow assemblage consisting of a single surface piercing vertical column and two submersible horizontal outriggers attached to the single surface piercing vertical column and oriented orthogonally with respect both to the single surface piercing vertical column and to each other.
 22. The buoyant structure of claim 1, wherein the one or more decks comprise a multilevel deck superstructure, wherein the submersible horizontal outriggers are supported at mid span by diagonal lower chord truss bracing tied into the surface piercing vertical columns at the multilevel deck superstructure.
 23. The buoyant structure of claim 1, wherein the hull comprises redundant internal bulkheads that enhance survivability of the structure in case of flooding due to hull damage.
 24. The buoyant structure of claim 1, wherein the hull comprises tankage and piping for liquid or gas storage.
 25. The buoyant structure of claim 1, further comprising accommodation, recreation and office facilities either in a deckhouse or below deck.
 26. The buoyant structure of claim 1, wherein the hull comprises storage or ballast tanks, internal accommodation spaces, machinery, and electrical and mechanical equipment.
 27. A method of dissipating wave forces before they reach the hull of the buoyant structure of claim 21, comprising operationally adjusting freeboard or depth of the elbow assemblages to break wave crests.
 28. A method of controlling dynamics of the buoyant structure of claim 1, comprising using differential ballasting to adjust the displacement and freeboard of the buoyant structure to maintain hydro-dynamic tuning for changing wave conditions or to provide additional freeboard for storm survival, or to maintain constant displacement at variations of hull and deck loading.
 29. The buoyant structure of claim 14, further comprising tubular vertical and diagonal braces, wherein trusses connect orthogonally at “K” type joints to provide bi-directional load bearing capacity. 